1. Field of the Invention
The present invention relates to alarm devices and in particular to such a device for sensing a change in a given parameter such as the temperature in a freezer, freezer compartment or the like from a predetermined safe level and for providing an alarm signal indicative thereof.
2. Description of the Prior Art
Numerous applications of alarm circuits exist. For example, among the many appliances that have received wide acceptance in the home, one of the most common and important appliances is the home freezer or combination refrigerator-freezer. Such freezers enable a household to purchase significant quantities of foods in bulk quantities to take advantage of special sales and similar cost and convenience buying practices. Accordingly, it is not at all uncommon for the owner of a freezer to have stored therein a quantity of food representing a substantial financial investment.
Frequently, the freezer, refrigerator or the like used to store food for a long period of time is situated remote from the kitchen or other high traffic areas of a home, such as for example in a garage or basement. In the event of a power failure or mechanical breakdown of the freezer, it is important that the owner take prompt steps to prevent the freezer interior from rising above a predetermined safe temperature which may result in loss of some or all of the foods stored therein. In the event of a power failure, the owner of a freezer is of course aware of the situation. However, it is not uncommon for the owner of a freezer to forget that the freezer is inoperative during these periods and losses of frozen foods often results. In the event of a mechanical failure of the freezer itself, the owner is frequently totally unaware of the situation until he opens same and finds that the contents have thawed and/ or spoiled. In a similar manner, sensing a change in temperature near a ceiling can be utilized for a fire alarm. Substituting a door or window switch, or a pressure sensitive switch for the temperature sensor enables use of an alarm circuit as a burglar alarm or a pump failure alarm.
There is therefore a need for a simple, easily mounted device which is inexpensive and can be easily adapted to provide an audible or other alarm indicative that a predetermined parameter has changed or shifted from a safe limit.